15 replies to this topic

[Zage]

I was wondering about Hydrostatic drives, what are they?, How do they work? ect. I have never seen or heard of them before, any info will be great.

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This post has been edited by Zage: 25 February 2005 - 11:25 AM

[Mike]

the river run gondola at keystone colorado has a hydrostatic aux drive. look at the bullwheel and you'll see the hydraulic motors that swing into the bullwheel. from what I hear, it works OK. I like the idea of being able to evac it with a blown gearbox. I think that it is very complicated and looks like it will be noisy, though.

[liftmech]

It isn't all that complicated, really. A hydrostatic system is as follows, for those not familiar with it. A diesel engine drives a hydraulic pump, which pushes fluid up (or down, as the case may be) to a hydraulic motor, which in turn drives the bullwheel by means of a ring-and-pinion set. It is exactly the same system as is found driving snowcats. In fact, some lifts have the motor, but not the pump; the pump is provided by connecting hoses to a snowcat's auxiliary plumbing ports.
I also like the idea of evacuating a lift in the event of a gearbox failure, seeing as we recently had one.

[Allan]

And hydraulic motors are very quiet.

[Mike]

The motors are quiet but are the straight cut gears noisy? I've never heard it run so I was just assuming that multiple motors and straight cut gears (not a ring and pinion) would have been noisy. The system I've seen at keystone looks rather complicated since it has mulitple motors and pumps and each motor needs it's own hydraulic lines and monitoring devices. I feel it creats more points of failure than a direct drive system via gearbox.

[Mike]

liftmech, on Feb 25 2005, 09:51 PM, said:

In fact, some lifts have the motor, but not the pump; the pump is provided by connecting hoses to a snowcat's auxiliary plumbing ports.<{POST_SNAPBACK}>

that is a neat way for resorts with limited budgets to have a way to evac the lift!

[Duck]

I don't think I've ever encountered a hydrostatic drive that I thought was quiet. :) They're quite common in the amusement industry and typically are at least moderatley noisy. But it's a good noise. Sounds neat. :)

If multiple motors are used on a drive wheel they're likely just connected in parallel to a single supply line going back to one or more pumps. Because of the nature of the drive, the load will be shared equally by all motors.

Here are 2 of my favourite applications of hydraulic drives. The huge haul winch on Dragster at CP - 32 hydraulic motors running off of huge nitrogen accumulators wind in a rope drum hauling the train up to 200 km/h in 4 seconds. You wouldn't beleive the noise the tiny sheaves make as the train roars past at top speed. :)

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Second is the huge Jump2 up here in Canada which has a 9 MW hydraulic drive that is used to fire a massive cylinder. Has a 30 000 L/min proportional valve (its servohydraulic).

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-Iain

[Doppeldork]

In canada all fixed grip and detachables have to have an evac drive aside from the main drive. The evac drives are used to run the load off if there ever is a main drive failure. Most of the newer lifts use a hydrostatic drive to do this. All a hydrostatic drive is a small deisel engine with a hydraulic pump. The pump powers a small hydraulic motor. I can only speak of Poma and Doppelmayr setups, but most are linked to the input shaft of the gearbox via a belt or 3. The snow cat option works well, but for bigger resorts sometimes that is logistically unrealistic.

[Doppeldork]

Mike, on Feb 25 2005, 03:13 PM, said:

the river run gondola at keystone colorado has a hydrostatic aux drive. look at the bullwheel and you'll see the hydraulic motors that swing into the bullwheel. from what I hear, it works OK. I like the idea of being able to evac it with a blown gearbox. I think that it is very complicated and looks like it will be noisy, though.
<{POST_SNAPBACK}>

So if the bullwheel is still connected to the gearbox, how do you turn the lift, if the gearbox is seized. And how does a hydraulic motor turn a bullwheel without the mechanical advantage of a gearbox, the pump and motor would have to be huge

This post has been edited by Doppeldork: 27 February 2005 - 08:43 AM

[Duck]

Doppeldork, on Feb 27 2005, 12:40 PM, said:

And how does a hydraulic motor turn a bullwheel without the mechanical advantage of a gearbox, the pump and motor would have to be huge

...and therin lies the immediate advantage of hydraulic drives. A small displacement in the pump and large displacement in the hydraulic motor automatically gives you a mechanical advantage. If the pump has a displacement of 0.1 L/r, and the motor has a displacement of 1 L/r, you have a 10:1 mechanical advantage. The pump can be very tiny. Hydrualic motors are more compact per unit of torque than equivelant types of drives (ICE, electric + gear reducer).

-Iain

[Mike]

Doppeldork, on Feb 27 2005, 09:40 AM, said:

So if the bullwheel is still connected to the gearbox, how do you turn the lift, if the gearbox is seized. And how does a hydraulic motor turn a bullwheel without the mechanical advantage of a gearbox, the pump and motor would have to be huge
<{POST_SNAPBACK}>

The gondala at keystone has two gearboxes. One in the vault that is connected to a medium speed shaft that goes to a planetary gearbox that sits above the bullwheel. The medium speed shaft can be disconected from the gearbox rather easily (a couple bolts). If the gearbox is siezed, the hydraulic motors are moved into the bullwheel and away it goes!. The mechanical advantage is like Duck said. Now that I think about it, the hydraulic motors will be turning rather slow (I'm guessing around 300 RPM) so the noise might not be too bad. There are multiple motors at keystone lift so that also spreads the load.

[liftmech]

Also, keep in mind we're talking about an evacuation-only drive. In the States there in a time limit on how long an evacuation may take if it is a lift-turning evac; I think it's an hour start-to-finish. So except for longer lifts, the hydrostatic drive can sacrifice speed for power. For an example the Flyer would have to run at only 166 FPM for an evac to take an hour.

[Doppeldork]

So if you have a time limit on "lift turning evacs" Do you have a time limit on rope evac? Just trying to understand their reasoning behind that, seen as how most rope evacs on a fully loaded quad or six pack take well over that amount of time.

[liftmech]

I think it's something to do with prep time or lead time for a rope eveac. It takes time to get personnel and equipment in place for a rope evac, whereas an aux evac can be gotten underway much faster. That hour could be used to get people and gear in place and begin taking people out of chairs. That could be an area-to-area decision, as well. My recollection of the rules is a bit rusty.

[Zage]

So really, it is the hydraulic motor powerd by the APU.

[Allan]

There's APUs and there's evac drives. APUs are capable of running the lift at or near normal speed, where as evac drives are just for evacuating passengers, and may not be very fast. All drives must be independently powered.